1. Field of the Invention
The invention relates in general to electrical inductive apparatus, such as transformers, and more specifically to electrical inductive apparatus having a magnetic core containing amorphous metal.
2. Description of the Prior Art
The core losses in the electrical transformers used by electric utility companies represents a significant loss of the energy generated, even though transformers are highly efficient. With the increasing value of energy, ways of reducing these loses are being sought. The use of amorphous metal in the magnetic cores of distribution and power transformers appears to be attractive, because, at equivalent inductions, the core losses of electrical grade amorphous metals are only 25% to 35% of the losses of conventional grain-oriented electrical steels.
Amorphous metals, however, in addition to their higher initial cost than conventional electrical steels, also pose many manufacturing problems not associated with conventional steels. For example, amorphous metal is very thin, being only about 1 to 11/2 mils thick, and it is very brittle, especially after anneal. Thus, with the wound magnetic cores conventionally used with distribution transformers, the core joint becomes a problem, making the use of a jointless magnetic core very attractive. This means that the primary and secondary windings of the transformer must be wound about the legs of a closed loop magnetic core. In order to utilize windings which are similar to those presently used in distribution transformers, the wound core would have to be wound and annealed in a rectangular configuration. This leads to another disadvantage of amorphous metals. The magnetic core, after winding, cannot support itself. It will collapse and close the window if oriented with the window axis horizontal. Amorphous metal is also very stress sensitive. Any pressure on the magnetic core, or change in its configuration after annealing, will increase its losses.
My concurrently filed application Ser. No. 699,378, filed Feb. 7, 1985, entitled "A Magnetic Core and Methods of Constructing Same", is directed to methods and coatings for making an amorphous core self-supporting, as well as to contain amorphous flakes and particles which may be associated with the core due to its brittleness. This copending patent application discloses the use of fiberglass reinforced composite coatings of low stress and high-strength resins, bonded to the flat, exposed lamination edges of a wound, unjointed magnetic core.
Making an amorphous magnetic core self-supporting, however, solves only part of the problem. Care must be taken not to exert stresses on the magnetic core during the coil winding process, during which the primary and secondary windings are wound directly on the winding legs of the magnetic core. Care must also be taken not to exert stresses on the magnetic core when it is immersed in a liquid-filled transformer tank and operated over many years of service.